Last year I made a last minute decision to join the Womens March in Downtown LA. To some degree I was a bit of just an observer since I went with no signs of my own and was by myself, though I figured even just being there was still a show of support. A couple weeks later, when the Muslim Ban was announced, protests materialized at airports, and being so close to LAX, it only made sense to go to that, too. Needing a quick but easy sign, I ended up coming up with this design using things I happened to have on hand. I used the same design for more signs later in the Resist March and figured I'd post it as an easy option to make a small and easy-to-carry sign. A key point here is that this is a small sign - not one that will make a big impression, but its compact size and lack of poles make it easy to carry around or travel with as a passenger in a car or on a subway.
I used a brown cardboard box that something had been shipped to me in - the sides happened to be 12x12.5 inches, so that became the size of the sign. It wasn't intentional, but ended up being the perfect size. About 2 inches from the bottom, I cut the top edge of a rectangular hole about 4 inches long and 2/3 of an inch high. A key point here is to only cut fully through on the top and sides of the hole, then score the bottom edge of the hole and bend it back as a flap without fully cutting it - that folded flap helps to make a more comfortable edge where you'll be holding the sign. For your message, obviously write or draw anything you want on both sides. If you want a pre-designed message, you can print a standard letter size 8.5x11" page and glue it to each side of the cardboard. I've uploaded a couple printable designs here that you can print out, too, and may occasionally add more to that link. If you have a phrase you'd like me to make a design for, please feel free to leave a request in the comments and I'll do my best to add it to the link: printable 8.5x11 signs. Of course, feel free to use those in your own way and share them, too.
There's your sign.